The Elemental Surge tempered affix seems to have some weird things going on with it that cause it to completely stop working. The only post I could find about it was a brief one from 4 days ago, so I’ll expound upon what I’ve seen so far. It seems as though once you stack a certain amount of 1 element type on your character the proc just stops working entirely. It happens both by using multiple weapons to stack 1 element or if the affix on 1 weapon gets upgraded through mastercrafting over a certain amount.
I first ran into this on Barb, which has 4 weapons slots (2x1h low affix, 2x2h high affix). I tried different combinations of putting affixes on 2x2h, 2x1h, 1h+2h, and with multiple element types at once, and once you reach a certain threshold for 1 Element type it stops proccing, while the others will still work (if they are below the cap).
I then had a 2h Scythe on my Necro that I tried masterworking and if the Elemental Surge Proc gets the random 25% upgrade it will exceed the cap and stop working. The first time the affix upgraded and I saw it, it then actually completely disappeared off the weapon and I thought I had accidentally tempered to something else instead of masterworked. It went down to 4 affixes, which I thought might be a visual bug so I tested dmg and relogged and it was like it didnt exist, and I thought I actually completely lost the shadow damage proc that I needed. But once I reset the masterwork it reappeared again.
I continued to masterwork and reset until I had gotten the 25% on the Elemental proc again and got it all the way to like 68.4k or something. And visually it stayed on this time, but upon testing it again would no longer proc. It seems to be capped at somewhere around 58k+, as I spent tons of mats until I fully upgraded the 2h Scythe without getting the 25% boost on the Elemental proc, and can confirm that it works at least up to the 55.1k amount that is on there now.
TLDR: Stacking a single element type from Elemental Surge tempering affix to >55.1k (roughly), causes it to completely bug out and stop working, whether that is on a single weapon or across multiple. I’m not sure if there is an intended cap or not, but it definitely wasted a lot of mats/tempered rolls not knowing that it would completely stop working at a certain point. Especially trying to masterwork an item WITHOUT randomly getting the Elemental Surge upgraded, because it would then be useless.
Edit: retested on Barb with different amounts 2h (45k) + 1h (23k), worked at 68k. So maybe that’s the cap, since 68.4k on Necro didn’t work. And adding another 1h (23k) to Barb causes it to stop working.